The idea of the "Universe Being Constant and Eternal", itself has no essence and contradicts natures own principle of Nothing is permanent. Though there were many theories in past these two theories Big Bang Theory and Steady-State Theory were widely considered scientific communities, moreover, very recently in the year 1993, Quasi-steady state cosmology (QSS) was suggested by a group of three scientists, this model depicts creation happening within our existing universe, the mini-bangs, little bangs, if not big bangs.
RE: Big Bang Theory or Steady State Theory